Piezoelectric vibrator and manufacturing method thereof

ABSTRACT

A piezoelectric vibrator has a container having a hermetically sealed cavity and a transparent portion for transmitting therethough a laser beam into the hermetically sealed cavity. A piezoelectric vibrator piece is disposed in the hermetically sealed cavity. A gettering substance is disposed directly on a surface of the piezoelectric vibrator piece so that when a laser beam is irradiated on the metal film through the transparent portion of the container the metal film is vaporized to absorb any gases contained in the hermetically sealed cavity of the container to thereby increase a degree of vacuum within the hermetically sealed cavity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric vibrator which isutilized for mobile information technology devices.

2. Backgound Information

In order to increase a degree of vacuum of a container which containsthe piezoelectric vibrator, a method in which baking is done in vacuumbefore hermetic-sealing and a substance of a factor decreasing thedegree of vacuum such as moisture adhering on surfaces of materials isremoved has been conventionally used. In order to remove gas trappedinside the container, a method in which a small hole opened beforehandin the container is closed in vacuum by a technique generating littlegas has been used.

In the method in which degassing is done by the baking before sealing,the gas generated during a sealing process is trapped in the container.Accordingly, oxygen, which is generated in case that the sealing is doneby anode bonding, is trapped in the container to decrease the degree ofvacuum. This results in an increase in equivalent series resistance R1.In case that the equivalent series resistance R1 is increased, such aproblem is generated that battery life is decreased, when thepiezoelectric vibrator is used for mobile devices. In the method inwhich the small hole opened beforehand in the container is closed invacuum, another process different from the sealing process, in which thesmall hole is closed, is required, so that man-hour is increased.

SUMMARY OF THE INVENTION

In order to solve the above-described problems, in a piezoelectricvibrator of the invention, a gettering substance for gettering inner gasis provided in a sealed space formed by a hermetic container in whichthe piezoelectric vibrator piece is arranged. The gettering substance isformed on a surface of the piezoelectric vibrator piece or an insidewall of the hermetic container. A metal film made of at least a kind ofmetal or its alloy selected from a group of aluminum, titanium, andzirconium is used as the gettering substance.

A manufacturing method for the piezoelectric vibrator of the inventionincludes a process in which an electrode for oscillation and the metalfilm for gettering gas are formed simultaneously on the piezoelectricvibrator piece, a process in which the piezoelectric vibrator piece isheld in the hermetic container and the hermetic container ishermetic-sealed, and a process in which the metal film is heated by alaser beam from outside to perform gettering of the inner gas of thehermetic-sealed container. Another manufacturing method for thepiezoelectric vibrator of the invention includes a process in which themetal film for gettering is provided inside the hermetic container whichcontains the piezoelectric vibrator piece, a process in which thehermetic container is hermetic-sealed so that the piezoelectric vibratorpiece is sealed inside the container, and a process in which the laserbeam is irradiated from outside onto the metal film to perform getteringof the inner gas of the hermetic-sealed container.

As described above, as the method for gettering gas in the containerafter sealing, the gettering substance is provided in the container andthen the gettering substance is irradiated from a transparent portion ofthe container by a YAG laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a first embodiment of the invention;

FIG. 2 is a sectional view showing a modification of the firstembodiment of the invention;

FIG. 3 is a sectional view showing a second embodiment of the invention;

FIG. 4 is a sectional view showing a modification of the secondembodiment of the invention;

FIG. 5 is a sectional view showing another modification of the secondembodiment of the invention;

FIG. 6 is a plan view showing a tuning fork type flexure vibrator usedin the embodiments of the invention;

FIG. 7 is a perspective view showing laser irradiation to a metal film;and

FIG. 8 is a graph showing a relationship between the number of lines oflaser irradiation and an equivalent series resistance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a piezoelectric vibrator of the invention, a gettering substance forgettering inner gas is provided on an inside wall of a hermeticcontainer having the piezoelectric vibrator piece inside or a surface ofthe piezoelectric vibrator piece which is arranged in the hermeticcontainer. A metal film made of at least a kind of metal or its alloyselected from a group of aluminum, titanium, and zirconium is suitablefor the gettering substance. An electrode for oscillation is also formedon the piezoelectric vibrator piece. The electrode for oscillation maybe also formed by the same material as the metal film for gettering. Byusing the above-described structure, gettering the gas in the hermeticcontainer is performed, so that a decrease in a degree of vacuum can beprevented.

Another piezoelectric vibrator of the invention includes a piezoelectricvibrator plate in which a piezoelectric vibrator piece and a frameportion surrounding a periphery of the piezoelectric vibrator piece areintegrally formed at a base portion of the piezoelectric vibrator piece,a cover which is bonded to the piezoelectric vibrator plate by the anodebonding through the metal film which is provided on a top surfaces ofthe frame portion, the container which is bonded to the piezoelectricvibrator plate by the anode bonding through the metal film which isprovided on a bottom surfaces of the frame portion, and the getteringsubstance which is provided on a surface of the piezoelectric vibratorpiece. The electrode for oscillation is also formed on the surface ofthe piezoelectric vibrator piece. It is desirable to use the metal filmas the gettering substance. In case that a weight for adjustingfrequency is provided on the piezoelectric vibrator piece, the weight isprovided at an end portion side of the piezoelectric vibrator piece soas to separate from the metal film for gettering arranged on the surfaceof the piezoelectric vibrator piece. By using the above-describedstructure, gettering the gas in the hermetic container is performed, sothat a decrease in a degree of vacuum can be prevented.

A manufacturing method for the piezoelectric vibrator of the inventionincludes a process in which the electrode for oscillation and the metalfilm for gettering gas are formed on the piezoelectric vibrator piece, aprocess in which the piezoelectric vibrator piece is held in thehermetic container having a transparent portion and the hermeticcontainer is hermetic-sealed, and a process in which the metal film isheated by the laser beam from outside through the transparent portion ofthe container to perform gettering of the inner gas of thehermetic-sealed container. According to the method, the metal is heatedby the laser irradiation to be vaporized. The vaporized metal iscombined with the oxygen in the container to be a metal oxide, whichresults in a decrease in the oxygen in the container and an increase inthe degree of vacuum of the container. For example, in case that theelectrode made of aluminum is irradiated by the laser beam, thevaporized aluminum is combined with the oxygen to be aluminum oxide,which causes the degree of vacuum of the container to be increased. Al,Ti, Zr or an alloy of these metals may be used as the metal.

There may be a method in which the metal film for gettering is formedinside the hermetic container of the piezoelectric vibrator, and thenafter hermetic-sealing, the metal is heated by the laser beam fromoutside through the transparent portion of the container to performgettering of the inner gas of the hermetic-sealed container.

(First Embodiment)

A first embodiment of the invention will be described on a basis offigures.

A piezoelectric vibrator of the first embodiment will be describedreferring to FIGS. 1 and 2. As shown in FIGS. 1 and 2, the piezoelectricvibrator of the embodiment includes a piezoelectric vibrator plate inwhich a quartz resonator piece (a vibrator piece) 2 and a frame portionsurrounding a periphery of the quartz resonator piece are integrallyformed at a base portion of the quartz resonator piece, a glass cover 3,and a glass cover or container 6. With using the anode bondingtechnique, the upper frame portion of the piezoelectric vibrator plateis bonded to the glass cover 3 and the glass container 6 by a metal film(not shown) which is provided on a top and a bottom surfaces of theframe portion. This allows the quartz resonator piece 2 to have astructure disposed in a hermetically sealed cavity 10 defined by theglass cover 3 and the glass container 6.

FIG. 1 is a schematically sectional view of a piezoelectric vibrator inwhich a metal film 1 as the gettering substance is arranged on a bottomsurface of the quartz resonator piece 2. A laser beam 7 is irradiatedfrom a top surface of the glass cover 3, the laser beam 7 transmitsthrough the glass cover 3 and the quartz resonator piece 2 to heat themetal film 1, the vaporized metal absorbs oxygen in the sealed space,consequently a degree of vacuum of the sealed space can be raised. Inthe embodiment, Aluminum is used as the metal film.

FIG. 2 shows a structure in which the metal film as the getteringsubstance is formed on a bottom surface of the glass cover 3. The laserbeam 7 is irradiated from the top surface of the glass cover 3, themetal film 1 is heated, the vaporized metal absorbs oxygen in the sealedspace, consequently the degree of vacuum of the sealed space isimproved. In the structure shown in FIG. 2, since the metal film 1 isnot formed on the quartz resonator piece 2, vibrating characteristics ofthe quartz resonator piece 2 are not varied by the gettering, so that adesign of the vibrator is simplified.

FIG. 1 and FIG. 2 are a type of piezoelectric vibrator in which thevibrator is hermetic-sealed in the glass container by using the anodebonding technique. On a principle of the anode bonding, oxygen isgenerated in bonding. The generated oxygen decreases the degree ofvacuum in the container and deteriorates characteristics of thepiezoelectric vibrator. Particularly, the equivalent series resistanceis increased. Therefore, the laser beam is irradiated to the metal filmarranged in the container, and the oxygen in the container is absorbedby heating the metal film, which allows the equivalent series resistanceto be reduced.

(Second Embodiment)

A piezoelectric vibrator of a second embodiment will be described on abasis of FIGS. 3 to 5. As shown in FIGS. 3 to 5, the piezoelectricvibrator of the embodiment is a vibrator in which the quartz resonatorpiece is mounted in a ceramic container and sealed by the glass cover.That is to say, the piezoelectric vibrator has a structure in which asupport portion is provided in a ceramic container 4, a base portion ofthe quartz resonator piece 2 is fixed to the support portion, and theglass cover 3 is arranged on a surface of the ceramic container 4.

In the piezoelectric vibrator shown in FIG. 3, the metal film 1 isformed on a top surface of the quartz resonator piece 2. In thepiezoelectric vibrator of the embodiment shown in FIG. 4, the metal film1 is formed on the bottom surface of the quartz resonator piece 2. FIG.5 is the embodiment in which the metal film 1 is formed on both the topand bottom surfaces of the quartz resonator piece 2. In the same way asin the first embodiment, the same effect can be obtained that the oxygenin the container is absorbed and the equivalent series resistance isreduced as in the first embodiment, in such a manner that the laser beamis irradiated to the metal film 1 for gettering through the glass fromthe top surface of the glass cover.

In each embodiment described above, a tuning fork type flexure vibratorhaving a shape shown in FIG. 6 is arranged. Additionally, a vibratorhaving a thickness shear mode is also applicable. An electrode foroscillation and a weight portion 5 for adjusting frequency are providedin an edge portion of the quartz resonator piece 2. The metal film 1 forgettering the oxygen is formed closer to a side of the base portion thanthe weight portion 5 for adjusting frequency. A metal material which iseasily oxidized such as aluminum, titanium, zirconium, and an alloycontaining these metal elements can be used as the metal film. An Al—Sialloy or an Al—Cu alloy can be used as the metal film. Particularly theAl—Cu alloy containing 1% to 5% of Cu can be used. The metal film may beformed on any one of the top surface side, bottom surface side, and boththe sides of the quartz resonator piece. In the embodiments, the metalfilm 1 made of aluminum is deposited by a sputtering method. Afterhermetic-sealing, when the laser beam is irradiated onto the metal filmfor gettering as shown in FIG. 7, the sputtered film made of aluminum isvaporized momentarily. At this point, the aluminum is bonded to theoxygen in the container to be aluminum oxide. The aluminum oxide isevaporated on an inside of the glass of the container. As a result, highvacuum is obtained in the container. Though a little vaporized materialis evaporated also on the quartz resonator, an electric short circuitnever occurs because the evaporated material on the quartz resonator isan oxide film. Because the oxide film is a fine particle, frequencyshift caused by the fell-out particle neither occurs. Furthermore, astable state of the oxide film prevents gas from returning in to thecontainer. FIG. 8 is a graph showing a variation in the equivalentseries resistance according to the invention. It is found from FIG. 8that the equivalent series resistance is sufficiently reduced by severallines of the laser irradiation.

In case that the above-described method is applied to the manufacturingmethod for the piezoelectric vibrator having the structure describedabove, man-hour is hardly increased, because the metal film forgettering is irradiated by the laser beam before the weight portion istrimmed by the laser in order to finely adjust the frequency.

As described above, according to the invention, the gas which exists inthe sealed container can be absorbed by heating the gettering substanceprovided in the sealed container, so that the vibration characteristicsof the piezoelectric vibrator can be improved even though pressure inthe container is increased by the anode bonding and the like todeteriorate the vibration characteristics.

1. A piezoelectric vibrator comprising: a container having hermeticallysealed cavity and a transparent portion for transmitting therethrough alaser beam into the hermetically sealed cavity; a piezoelectric vibratorpiece disposed in the hermetically sealed cavity; a gettering substancecomprised of a metal film disposed directly on a surface of the sealedpiezoelectric vibrator piece so that when a laser beam is irradiated onthe metal film through the transparent portion of the container, themetal film is vaporized to absorb any gases contained in thehermetically sealed cavity of the container to thereby increase a degreeof vacuum within the hermetically sealed cavity; and a weight disposedon the piezoelectric vibrator piece in spaced-apart relation to themetal film.
 2. A piezoelectric vibrator comprising: a piezoelectricvibrator plate in which a piezoelectric vibrator piece and a frameportion connected with a base portion and surrounding the piezoelectricvibrator piece, the frame portion having a first main surface and asecond main surface opposite the first main surface; a cover connectedto the piezoelectric vibrator plate by anodic bonding through a firstmetal film disposed on the first surface of the frame portion of thepiezoelectric vibrator plate; a container which is bonded to thepiezoelectric vibrator plate by anode bonding through a first metal filmdisposed on the second main surfaces of the frame portion of thepiezoelectric vibrator plate; and a gettering substance disposeddirectly on a surface of the piezoelectric vibrator piece.
 3. Apiezoelectric vibrator as claimed in claim 2; wherein at least one ofthe cover and the container is made of glass.
 4. A piezoelectricvibrator as claimed in claim 2; wherein the gettering substancecomprises a third metal film.
 5. A piezoelectric vibrator as claimed inclaim 4; wherein the third metal film is made of a material selectedfrom the group consisting of aluminum, titanium, zirconium, an aluminumalloy, a titanium alloy, and a zirconium alloy.
 6. A piezoelectricvibrator comprising: a piezoelectric vibrator plate having apiezoelectric vibrator piece; a pair of cover members connected togetherand forming a hermetically sealed cavity containing the piezoelectricvibrator piece of the piezoelectric vibrator plate in a state in whichthe piezoelectric vibrator piece is capable of undergoing oscillatingmovement; and at least one gettering substance disposed directly on asurface of one of the piezoelectric vibrator piece.
 7. A piezoelectricvibrator as claimed in claim 6; wherein the gettering substancecomprises a metal film.
 8. A piezoelectric vibrator as claimed in claim6; wherein at least one of the cover members has a transparent portionfor transmitting therethrough a laser beam into the hermetically sealedcavity; and wherein when a laser beam is irradiated on the getteringsubstance through the transparent portion of the cover member, thegettering substance is vaporized to absorb any gases contained in thehermetically sealed cavity to thereby increase a degree of vacuum withinthe hermetically sealed cavity.
 9. A piezoelectric vibrator as claimedin claim 8; wherein the gettering substance comprises a metal film. 10.A piezoelectric vibrator as claimed in claim 6; wherein thepiezoelectric vibrator piece has a first main surface and a second mainsurface opposite the first main surface; and wherein the at least onegettering substance comprises a first gettering substance disposeddirectly on the first main surface of the piezoelectric vibrator pieceand a second gettering substance disposed directly on the second mainsurface of the piezoelectric vibrator piece.
 11. A piezoelectricvibrator as claimed in claim 10; wherein each of the first and secondgettering substances comprises a metal film.
 12. A piezoelectricvibrator comprising: a piezoelectric vibrator plate having apiezoelectric vibrator piece; a pair of cover members connected togetherand forming a hermetically sealed cavity containing the piezoelectricvibrator piece of the piezoelectric vibrator plate in a state in whichthe piezoelectric vibrator piece is capable of undergoing oscillatingmovement; and at least one gettering substance disposed in thehermetically sealed cavity directly on a surface of one of the covermembers.
 13. A piezoelectric vibrator as claimed in claim 12; whereinthe gettering substance comprises a metal film.
 14. A piezoelectricvibrator as claimed in claim 12; wherein at least one of the covermembers has a transparent portion for transmitting therethrough a laserbeam into the hermetically sealed cavity; and wherein when a laser beamis irradiated on the gettering substance through the transparent portionof the cover member, the gettering substance is vaporized to absorb anygases contained in the hermetically sealed cavity to thereby increase adegree of vacuum within the hermetically sealed cavity.
 15. Apiezoelectric vibrator as claimed in claim 14; wherein the getteringsubstance comprises a metal film.